However, minutes after Dean Fitzpatrick was stabbed, David Mahon (45) told his friend Karl O'Toole he thinks "Dean is dead" and "the knife went through him", prosecution counsel, Remy Farrell SC has said.

Mr Farrell has begun his closing speech in the trial of David Mahon, who has denied murdering 23-year-old Dean Fitzpatrick on May 26, 2013.

Mr Fitzpatrick is the brother of Amy Fitzpatrick who went missing in Spain in 2008.

The father-of-one was stabbed to death outside Mr Mahon’s apartment at Burnell Square, Northern Cross in Malahide.

In his closing speech, Mr Farrell told the Central Criminal Court that in some respects this case was not terribly complicated, and was about "a split second".

Mr Farrell said there was no contest about a lot of the evidence. There was no contest Mr Mahon had the knife in his hand and it entered Dean Fitzpatrick's abdomen, killing him, he said.

The jury was told it must decide on Mr Mahon's intent, "was it his intent to kill him, to cause him serious harm".

Mr Farrell told the jury "judge a man by his actions, judge a man by his words".

He said Mr Mahon spent the Saturday that Mr Fitzpatrick died "frenetically" trying to get in contact with his stepson.

He said there were 12 mobile phone calls from Mr Mahon to Mr Fitzpatrick between 9.40pm and 10pm on the Saturday night. There was also six calls to Dean's former girlfriend, Sarah O'Rourke.

Mr Farrell said it appears Mr Mahon was frenetically trying to get in touch with his stepson, and had sent him a text message earlier in the day threatening to stab him.

He told the jury we also know something about Mr Mahon's mood, with Ms O'Rourke telling the court he was "aggressive".

Mr Farrell said Ms O'Rourke told the jury Mr Mahon was looking for Dean and he threatened he would "stick a knife in her neck".

Mr Farrell said the defence has not suggested that Ms O'Rourke made up this threat.

The jury was also told that after Dean was stabbed Mr Mahon told his friend Karl O'Toole to get him out of the apartment.

The pair left in Mr O'Toole's taxi and they drove around north Dublin.

Mr Farrell said Mr O'Toole gave evidence that Mr Mahon said to him he thinks "Dean is dead" and he thinks "the knife went through him".

The jury heard that in the minutes after Mr Fitzpatrick's stabbing, Mr Mahon was giving "a very good impersonation of a man who has just admitted murder".

Mr Farrell said Mr Mahon told gardai "lie after lie after lie" in the five interviews which they conducted with him, and cooked up" a story that it had been a terrible and "wholly innocent accident".

Mr Mahon told gardai it wasn't his style to "run and hide" but that was exactly what he did by fleeing the scene, said Mr Farrell.

The jury heard that one of the biggest lies Mr Mahon told to gardai was that he didn't know how serious the injury was, as Mr O'Toole's evidence is that he had told him "Dean is dead".

Mr Farrell said Mr Mahon left Dean "to die on the street", while he threw away the murder weapon and drove around the roads of north Dublin.

He said that if Mr Mahon's defence is that of accident or suicide then he must be the "most unfortunate man in Ireland due to a confluence of remarkable events that put him in the wrong place at the wrong time".

Mr Farrell said that the reality was that Mr Mahon was drunk, angry and agitated and that he stabbed his stepson and then set about doing everything he could to try and "get away with murder".

Mr Farrell has now finished his closing speech.

Defence counsel, Sean Guerin SC, will begin his closing speech on Tuesday, and then the judge will give her charge to the jury.